1. Field of the Invention
The present invention relates to apparatus and processes for the production of food products from an extruded dough. More particularly, the present invention provides a novel extrusion die for continuously extruding a laminated, multi-layer dough mass from a single die opening.
2. Description of the Background Art
In the baked goods industry, it is common to produce baked goods, such as pastry products and crackers having a desirable "flaky" or multi-layered texture, by producing dough sheets that are overlaid to form a multi-layered dough mass. The dough mass subsequently is passed through one or more roll sets, or is compressed by a similar process, to produce a "laminated" dough mass. The laminated dough is reduced in overall thickness but, importantly, the compression process has not completely destroyed its multi-layer nature. Upon cooking under relatively stringent conditions (such as baking or frying), moisture in the form of steam that is released from the dough mass and causes partial delamination of the dough layers, producing a desired texture in the fully cooked product. The presence of a leavening agent, such as sodium or ammonium bicarbonate, also causes delamination during the cooking process. The final texture ultimately depends on the composition of the dough and the vigor with which the dough layers were laminated, among other variables.
As described in U.S. Pat. No. 4,675,199 issued to Nestec S. A. on Jun. 23, 1987, it has also been known to produce pasta products from laminated dough sheets so as to attain desirable eating qualities, that is, a less-dense mouth feel. The dough sheet can be produced in a manner similar to the pastry and cracker dough process described above, by folding a dough sheet many times and passing the folded sheet through rollers to flatten and compress the dough. The Nestec patent proposes to simulate such a process through the use of an extrusion die containing a plurality of openings for simultaneously extruding a plurality of continuous pasta dough sheets in a vertical orientation. The extruded sheets are united and compressed downstream of the die by one or more roller sets into a single sheet, which is then cut into a desired shape.
The same improvement to product texture--rendering the finished product lighter in texture, with a less-dense mouth feel--that is attained through the lamination technique is desired in the production of certain snack food products such as snack chips. It is known to those skilled in the art to produce snack food products, including various types of snack chips, by forming a dough mass, continuously extruding the mass in the form of a monolayer ribbon or other desired shape, cutting the monolayer extrudate into a desired size and shape, and then cooking and seasoning the product. The dough typically is extruded under low work conditions, and with a moisture content of about 25 to 45 percent (wet basis), to produce an extrudate that is stable enough to survive subsequent handling without breaking.
To produce a finished, monolayer product with consumer-acceptable texture, for example a light and less dense mouth feel, a relatively thin extrusion die thickness typically is needed. Snack food products prepared from relatively thick, extruded dough sheets tend to have a dense mouth feel and texture that is not favored by consumers. The use of a thin extrusion die opening, however, leads to numerous problems. The pressure of the dough mass will build at the die opening and, depending on the composition of the dough, this pressure increase will require excessive working of the dough mass by the extruder and will result in a high rate of breakage of the intermediate or finished product. The use of a thin extrusion die also will (1) cause increased work input to the dough, contributing to the undesired dense, tough texture; (2) cause increased occurrence of partially plugged die openings; (3) require smaller tolerances in the die opening machining and (4) increase the velocity of dough from the die, for example beyond the handling capability of conventional lamination rolls. Although the multi-layering processes described above have theoretical utility in the production of snack food products such as snack chips, the costs associated with those processes are prohibitive. Moreover, certain snack food product shapes (for example, those with rippled edges) do not lend themselves to production via such processes.